U.S. patent number 6,488,345 [Application Number 09/931,508] was granted by the patent office on 2002-12-03 for regenerative braking system for a batteriless fuel cell vehicle.
This patent grant is currently assigned to General Motors Corporation. Invention is credited to Martin Fasse, Peter Willimowski, George R. Woody.
United States Patent |
6,488,345 |
Woody , et al. |
December 3, 2002 |
Regenerative braking system for a batteriless fuel cell vehicle
Abstract
A regenerative braking system and method for a batteriless fuel
cell vehicle includes a fuel cell stack, a plurality of ancillary
loads, and a regenerative braking device that is coupled to at
least one wheel of the vehicle. The regenerative braking device
powers ancillary loads when the vehicle is coasting or braking. The
fuel cell powers the loads when the vehicle is accelerating or at
constant velocity. The regenerative braking device dissipates power
in an air supply compressor when the vehicle is traveling downhill
to provide brake assistance. The compressor can be run at high
airflow and high pressure to create an artificially high load. A
bypass valve is modulated to adjust the artificially high load of
the compressor. A back pressure valve protects the fuel cell stack
from the high airflow and pressure. A controller controls a brake
torque of the regenerative braking device as a function of vehicle
speed and modulates the bypass valve.
Inventors: |
Woody; George R. (Wiesbaden,
DE), Fasse; Martin (Wiesbaden, DE),
Willimowski; Peter (Darmstadt, DE) |
Assignee: |
General Motors Corporation
(Detroit, MI)
|
Family
ID: |
25460889 |
Appl.
No.: |
09/931,508 |
Filed: |
August 16, 2001 |
Current U.S.
Class: |
303/152; 180/165;
303/20; 701/22; 303/3; 188/158; 180/65.31; 429/444; 429/452 |
Current CPC
Class: |
B60L
58/34 (20190201); B60T 8/00 (20130101); B60L
58/30 (20190201); B60L 7/10 (20130101); B60L
58/33 (20190201); B60T 1/10 (20130101); B60K
1/04 (20130101); Y02T 90/34 (20130101); Y02T
90/40 (20130101) |
Current International
Class: |
B60L
7/10 (20060101); B60L 11/18 (20060101); B60T
1/10 (20060101); B60T 1/00 (20060101); B60T
8/00 (20060101); B60L 7/00 (20060101); B60K
1/04 (20060101); B60T 008/00 (); B60K 001/00 () |
Field of
Search: |
;303/152,2-3,20 ;701/22
;180/165,65.1-65.8,197 ;429/17,9,12,13,19,34,218.2,24-26
;318/139,376 ;320/101,104,147 ;60/413,414 ;188/156,158 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Butler; Douglas C.
Attorney, Agent or Firm: Barr, Jr.; Karl F. Brooks; Cary W.
Deschere; Linda M.
Claims
What is claimed is:
1. A regenerative braking system for a batteriless fuel cell
vehicle, comprising: a fuel cell stack; an ancillary load; and a
regenerative braking device coupled to at least one wheel of said
vehicle, wherein said regenerative braking device powers said
ancillary load when said vehicle is coasting or braking and wherein
said fuel cell powers said ancillary load when said vehicle is
accelerating or traveling at a constant velocity.
2. The regenerative braking system of claim 1 wherein said
ancillary load is selected from the group of fans, pumps,
airconditioning compressor, cabin heater, 12 volt battery, and an
air compressor for said fuel cell stack.
3. The regenerative braking system of claim 1 further comprising an
air compressor for said fuel cell stack.
4. The regenerative braking system of claim 3 further comprising a
bypass valve.
5. The regenerative braking system of claim 4 wherein when said
vehicle is traveling downhill, said air compressor is run at high
airflow and high pressure to create an artificially high ancillary
load and said bypass valve is modulated to vary said artificially
high ancillary load of said air compressor to provide brake
assistance.
6. The regenerative braking system of claim 5 further comprising a
back pressure valve that protects said fuel cell stack from said
high airflow and said high pressure.
7. The regenerative braking system of claim 5 further comprising a
controller.
8. The regenerative braking system of claim 7 wherein said
controller controls a brake torque of said regenerative braking
device as a function of vehicle speed.
9. The regenerative braking system of claim 7 wherein said
controller modulates said bypass valve.
10. The regenerative braking system of claim 1 wherein said
regenerative braking device is an electric traction system.
11. The regenerative braking system of claim 1 wherein when said
vehicle is coasting or braking, delivery of air and fuel to said
fuel cell stack is interrupted.
12. The regenerative braking system of claim 11 further comprising
a controller.
13. The regenerative braking system of claim 12 wherein said
controller sets a brake torque of said regenerative braking device
as a function of vehicle speed.
14. The regenerative braking system of claim 12 wherein said
controller modulates said bypass valve.
15. The regenerative braking system of claim 1 wherein said
regenerative braking device is an electric traction system.
16. A regenerative braking system for a batteriless fuel cell
vehicle, comprising: a fuel cell stack; an air compressor that
provides air to said fuel cell stack; a regenerative braking device
coupled to at least one wheel of said vehicle and to said air
compressor; and a bypass valve, wherein said air compressor is run
at high pressure and high airflow to create an artificial load on
said regenerative braking device, and wherein said artificial load
is modulated by said bypass valve.
17. The regenerative braking system of claim 16 further comprising
a back pressure valve for protecting said fuel cell stack when said
air compressor is dissipating said power.
18. A method for operating a batteriless fuel cell vehicle,
comprising the steps of: providing a fuel cell stack; providing air
to said fuel cell stack using an air compressor; coupling a
regenerative braking device to at least one wheel of said vehicle;
connecting a regenerative braking device to said air compressor;
and dissipating power that is produced by said regenerative braking
device when said vehicle is traveling downhill using said air
compressor.
19. The method of claim 18 further comprising the step of
modulating a bypass valve to adjust said power that is dissipated
by said air compressor.
20. The method of claim 19 further comprising the step of running
said air compressor at high airflow and high pressure to create an
artificial loss when said vehicle is traveling downhill.
21. The method of claim 20 further comprising the step of
modulating a back pressure valve that is connected to an outlet of
a cathode of said fuel cell stack to protect said fuel cell stack
when said air compressor is run at said high airflow and high
pressure.
22. The method of claim 19 further comprising the step of setting a
brake torque of said regenerative braking device as a function of
vehicle speed using a controller.
23. The method of claim 18 further comprising the step of
interrupting delivery of air and fuel to said fuel cell stack when
said vehicle is traveling downhill.
24. The method of claim 18 wherein said regenerative braking device
is an electric traction system.
25. The method of claim 24 wherein said controller modulates said
bypass valve.
Description
FIELD OF THE INVENTION
The present invention relates to fuel cells, and more particularly
to fuel cells that employ regenerative braking.
BACKGROUND OF THE INVENTION
Fuel cell systems are increasingly being used as a power source in
a wide variety of applications. Fuel cell systems have also been
proposed for use in vehicles as a replacement for internal
combustion engines. A solid-polymer-electrolyte fuel cell includes
a membrane that is sandwiched between an anode and a cathode. To
produce electricity through an electrochemical reaction, hydrogen
(H.sub.2) is supplied to the anode and oxygen (O.sub.2) is supplied
to the cathode. The source of the hydrogen is typically pure
hydrogen, reformed methanol, or other reformed hydrocarbon
fuels.
In a first half-cell reaction, dissociation of the hydrogen
(H.sub.2) at the anode generates hydrogen protons (H.sup.+) and
electrons (e.sup.-). The membrane is proton conductive and
dielectric. As a result, the protons are transported through the
membrane while the electrons flow through an electrical load that
is connected across the membrane. The electrical load is typically
a motor that drives the wheels of the vehicle or storage batteries.
In a second half-cell reaction, oxygen (O.sub.2) at the cathode
reacts with protons (H.sup.+), and electrons (e.sup.-) are taken up
to form water (H.sub.2 O). Therefore, fuel cell vehicles have
little or no emissions.
Internal combustion engine vehicles and hybrid vehicles sometimes
employ regenerative braking to improve the efficiency of the
vehicle. In non-regenerative braking vehicles, the torque produced
by the brakes causes friction that slows the wheels of the vehicle.
The friction creates waste heat that increases the temperature of
the brakes. Regenerative braking devices convert mechanical brake
torque that occurs during vehicle deceleration into power. The
energy that is produced by the brake torque is typically used to
recharge a battery pack that powers vehicle accessory loads such as
the lights, radio, pumps, air conditioner, fans, and other
devices.
In U.S. Pat. No. 4,489,242 to Worst, a vehicle power system
includes an internal combustion engine and a regenerative braking
device that charges a battery pack. The battery pack powers one or
more vehicle accessories such as vehicle lights, power steering and
brake pumps, air conditioner, radiator fan, water pump, etc. In
U.S. Pat. No. 5,345,761 to King et al., regenerative braking is
used to power a high-voltage, electrically-heated catalyst that
treats the exhaust gas of an internal combustion engine. In U.S.
Pat. No. 6,122,588, regenerative braking is used to supply power to
increase fuel efficiency and/or to power various electrical loads
such as vehicle accessories.
Regenerative braking is generally provided by a motor/generator
that opposes the rotation of the wheels by applying a negative or
regarding torque to the wheels of the vehicle. Because the negative
torque decelerates the vehicle and is often used to assist the
brakes, regenerative braking systems generally reduce the wear on
the brakes of the vehicle, which reduces maintenance costs.
Because fuel cell vehicles are relatively new in the automotive
arena, current fuel cells do not produce as much power as internal
combustion engines. Fuel cell vehicles are also more expensive than
internal combustion engines. Before widespread acceptance of fuel
cells will occur, these performance and cost issues must be
resolved. The performance of the fuel cell is related to the weight
of the fuel cell. Because of the increased weight and cost of
battery packs and DC/DC converters that are required in
regenerative braking systems, fuel cell have not implemented
regenerative braking systems.
SUMMARY OF THE INVENTION
A regenerative braking system and method for a batteriless fuel
cell vehicle includes a fuel cell stack, an ancillary load, and a
regenerative braking device that is coupled to at least one wheel
of the vehicle. The regenerative braking device powers the
ancillary load when the vehicle is coasting or braking. The fuel
cell powers the ancillary load when the vehicle is accelerating or
at constant velocity.
In other features of the invention, the regenerative braking system
includes an air compressor. The regenerative braking device
dissipates power in the air compressor when the vehicle is
traveling downhill to provide brake assistance. A bypass valve has
an inlet connected to the air compressor. When the vehicle is
traveling downhill, the air compressor is run at high airflow and
high pressure to create an artificial load. The bypass valve is
modulated to adjust the artificial load of the air compressor.
In still other features of the invention, the regenerative braking
device is an electric traction system. A back pressure valve is
connected to a cathode of the fuel cell stack. The back pressure
valve protects the fuel cell stack from the high airflow and
pressure. A controller controls a brake torque of the regenerative
braking device as a function of vehicle speed and modulates the
bypass valve to vary the artificial load.
Further areas of applicability of the present invention will become
apparent from the detailed description provided hereinafter. It
should be understood that the detailed description and specific
examples, while indicating the preferred embodiment of the
invention, are intended for purposes of illustration only and are
not intended to limit the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become more fully understood from the
detailed description and the accompanying drawings, wherein:
FIG. 1 illustrates a cross-section of a membrane electrode assembly
of an exemplary fuel cell; 4
FIG. 2 (prior art) is a functional block diagram illustrating an
internal combustion engine with batteries and a regenerative
braking device;
FIG. 3 is a functional block diagram showing a batteriless fuel
cell system with a regenerative braking device in accordance with
the present invention;
FIG. 4 illustrates steps for operating the batteriless fuel cell
system of FIG. 3;
FIGS. 5A, 5B and 5C are waveforms that illustrate regenerative
braking in the batteriless fuel cell system of FIG. 3;
FIG. 6 are waveforms that illustrate gross power and regenerative
power of a portion of the waveform in FIG. 5 in further detail;
and
FIG. 7 shows an exemplary alternate position for a bypass valve and
a backpressure valve.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following description of the preferred embodiment(s) is merely
exemplary in nature and is in no way intended to limit the
invention, its application, or uses.
Referring now to FIG. 1, a cross-section of a fuel cell assembly 10
that includes a membrane electrode assembly (MEA) 12 is shown.
Preferably, the MEA 12 is a proton exchange membrane (PEM). The MEA
12 includes a membrane 14, a cathode 16, and an anode 18. The
membrane 14 is sandwiched between an inner surface of the cathode
16 and an inner surface of the anode 18.
A cathode diffusion medium 20 is located adjacent to an outer
surface of the cathode 16. An anode diffusion medium 24 is located
adjacent to an outer surface of the anode 18. The fuel cell
assembly 10 further includes a cathode flow line 26 and anode flow
line 28. The cathode flow line 26 receives and directs oxygen
(O.sub.2) or air from a source to the cathode diffusion medium 20.
The anode flow line 28 receives and directs hydrogen (H.sub.2) or
reformate from a source to the anode diffusion medium 24. Skilled
artisans will appreciate that the source of hydrogen is preferably
pure hydrogen, reformed methanol, a reformed hydrocarbon fuel, or
any other suitable hydrogen source.
In the fuel cell assembly 10, the membrane 14 is a cation
permeable, proton conductive membrane having H+ ions as the mobile
ion. The fuel gas is hydrogen (H.sub.2) and the oxidant is oxygen
(O.sub.2). The overall cell reaction is the oxidation of hydrogen
to water and the respective reactions at the anode 18 and the
cathode 16 are as follows:
Since hydrogen is used as the fuel gas, the product of the overall
cell reaction is water. Typically, the water that is produced is
rejected at the cathode 16, which is a porous electrode including
an electrocatalyst layer on the oxygen side. The water may be
collected as it is formed and carried away from the MEA 12 of the
fuel cell assembly 10 in any conventional manner. The cell reaction
produces a proton exchange in a direction from the anode diffusion
medium 24 towards the cathode diffusion medium 20. In this manner,
the fuel cell assembly 10 produces electricity. An electrical load
30 such as a motor, vehicle accessories, or other device is
electrically connected to the MEA 12 to a plate 32 and a plate 34.
If the plates 32 and 34 are adjacent to another fuel cell, the
plates 32 and/or 34 are bipolar. If another fuel cell is not
adjacent, the plates 32 and/or 34 are end plates.
Referring now to FIG. 2, a vehicle 50 that includes a storage
battery 52 is shown. A regenerative braking device 54 is coupled to
one or more wheels 56 of the vehicle 50. The regenerative braking
device 54 generates power when the vehicle coasts (causing slight
deceleration), is traveling downhill, and/or when the driver
applies the brakes (to decelerate the vehicle). A power
distribution device 60 such as a high-voltage bus distributes the
power that is generated by the regenerative braking device 54. The
power distribution device 60 distributes power directly to one or
more loads 64 and/or recharges the storage battery 52 depending
upon the circumstances.
When the driver depresses the accelerator, an internal combustion
engine 70 generates power from air 72 and fuel 74 that is supplied
to the engine 70. When the vehicle is coasting or braking to reduce
speed, the regenerative braking device 54 generates power that can
be used to charge the storage battery 52 and/or to power the loads
64. Oftentimes, the storage battery 52 provides power to the
accessories at lower speeds and when the vehicle is stopped to
improve fuel efficiency of the vehicle.
Referring now to FIG. 3, a regenerative braking system for a
batteriless fuel cell vehicle is shown and is generally designated
100. The regenerative braking system 100 includes a regenerative
braking device 102 that is coupled to at least one wheel 104 of the
fuel cell vehicle. The regenerative braking device 102 is
preferably an electric traction system. The regenerative braking
system 100 includes a fuel cell stack 106 that includes an anode
flowline with an inlet 110 and an outlet 112. The fuel cell 106
also includes a cathode flowline 114 with an inlet 116 and outlet
118.
The regenerative braking system 100 further includes an air
compressor 124, a back pressure valve 126 and a bypass valve 128.
The bypass valve 128 is connected to an outlet of the air
compressor 124, a cathode of the fuel cell stack 106 and to the
environment. A power output of the regenerative braking device 102
is connected to a power distribution device 130 that is connected
to loads 134. The loads 134 preferably include fans, pumps, an air
conditioning compressor, heaters, 12 volt battery, and other
devices. The brake torque (and energy) provided by the regenerative
braking device 102 is preferably set as a function of vehicle
speed.
The air compressor 124 pressurizes supply air 140 and outputs the
pressurized air to the bypass valve 128. A controller 144 is
connected to the back pressure valve 126, the bypass value 128, the
compressor 124, and a vehicle data bus 148. The controller 144
modulates the bypass valve 128 to selectively divert the air to the
inlet 116 of the cathode flowline 114, to exhaust the air and/or to
direct the air to another device.
During normal driving when the vehicle's speed is greater than zero
and the vehicle is not accelerating or when the vehicle is at
constant velocity, the regenerative braking device 102 produces
power and the loads 134 dissipate the energy. During braking and
coasting, air and fuel to the fuel cell stack 106 are preferably
shut off and no fuel consumption occurs. As a result, the output of
the fuel cell stack is 0 kW during braking and coasting.
When driving downhill (detected by monitoring vehicle acceleration
and the position of the accelerator pedal through the vehicle data
bus 148), the regenerative braking device 102 powers the ancillary
loads. In a highly preferred mode, the controller 144 runs the
compressor with high airflow and high pressure to create an
artificial loss. During this condition, the back pressure valve 126
is either closed or partially opened (if additional power is
required from the fuel cell stack). The controller 144 controls the
back pressure valve 126 to prevent the high pressure air that is
generated by the air compressor 124 from reaching the fuel cell
stack 106. The controller 144 modulates the bypass valve 128 to
regulate a compressor load of the air compressor 124 and to
regulate the brake torque of the regenerative braking device
102.
Referring now to FIG. 4, steps for operating the controller 144 are
shown. Control begins with step 160. In step 164, the controller
144 determines whether the speed of the vehicle exceeds 0 km/hr. In
other words, the controller 144 determines whether the vehicle is
moving. If not, control loops to step 164. Otherwise, control
continues with step 168 where the controller 144 determines whether
the vehicle is coasting or braking. If not, control loops to step
164. Otherwise, the controller 144 continues with step 172 where
the fuel cell stack 106 is shut down by cutting off air and fuel
that is supplied to the fuel cell stack 106. In step 176, the brake
torque is set as a function of the speed of the vehicle. In step
180, the loads 134 are powered using the regenerative braking.
In step 184, the controller 144 determines whether the vehicle is
driving downhill by monitoring the position of the accelerator
pedal and the speed or acceleration of the vehicle via the vehicle
data bus 148. If the vehicle is not driving downhill, control loops
to step 164. Otherwise, control continues with step 184. In step
184, the controller 144 sets the compressor 124 to a high airflow
and high pressure setting to create an artificial loss that
dissipates the energy produced by the regenerative braking (and
that provides brake assist). In step 186, control determines
whether power is needed from the fuel cell stack 106. If not, the
controller 144 closes the back pressure valve 126 in step 190. If
power from the fuel cell is needed, the controller 144 modulates
the back pressure valve 126 accordingly in step 192.
Control continues from steps 190 and 192 to step 194. In step 194,
the controller 144 uses the bypass valve 128 to regulate the load
of the air compressor 124 and to regulate brake torque of the
regenerative braking device 102. Control continues from step 194 to
step 164.
Referring now to FIG. 5A, 5B and 5C, exemplary waveforms depicting
the vehicle speed, gross power, regenerative power, and mechanical
torque at the axle of the fuel cell vehicle is shown. In FIG. 5A,
vehicle speed increases from zero (at 200) to 20 km/hr (at 204).
Subsequently, the vehicle decelerates back to zero (at 206) and
then accelerates to 40 km/hr (at 208). The vehicle decelerates to
20 km/hr (at 210), accelerates to 40 km/hr (at 212), and then
decelerates to 20 km/hr (at 214). In FIG. 5B, the gross power is
shown with a dotted line (at 220). Regenerative power is shown with
the solid lines 224, 226, and 228. The regenerative power occurs
when the vehicle is coasting or braking. In FIG. 5C, the mechanical
torque at the axle is illustrated by solid line 230. The torque
occurs when the vehicle is accelerating, at constant velocity,
coasting (due to the regenerative brake device) or braking.
Referring now to FIG. 6, the gross power and regenerative power for
the area identified by the circular dotted line 240 in FIG. 5B is
shown in further detail. The power represented by the first region
242 is used to power the loads. The power represented by the second
region 244 is used for driver feel or feedback. The batteriless
regenerative braking system according to the present invention
significantly reduces the weight and cost of the fuel cell vehicle
while providing sufficient power to the loads during vehicle
coasting and braking using existing components. When traveling
downhill, the compressor is run at high pressure and high airflow
to create an artificial load and to provide brake assistance.
Skilled at artisans will appreciate that the batteriless fuel cell
vehicle may include a smaller battery (that does not power the
electric motor driving the wheels) that powers the accessories
while the vehicle is stopped.
Referring now to FIG. 7, the three-way bypass valve 128 of FIG. 3
can be replaced by an alternate system 248 that is shown in FIG. 7.
An inlet of a two-way bypass valve 250 is connected to the inlet
116 of the cathode 114 and to an outlet of the compressor 124. An
outlet of the bypass valve 250 is connected to a cathode exhaust
252. A backpressure valve 254 has an inlet connected to the outlet
118 of the cathode 114 and an outlet connected to the cathode
exhaust. The alternate system 248 creates an artificial load by
opening the bypass valve 250 and by closing the backpressure valve
254. The cathode side of the fuel cell stack 106 is now at high
pressure during operation of the artificial compressor load. Other
advantages include the use of a two-way valve that is typically
less expensive than the three-way bypass valve. Skilled artisans
will appreciate that the bypass and backpressure valves can be
positioned in other locations without departing from the spirit and
scope of the invention.
Those skilled in the art can now appreciate from the foregoing
description that the broad teachings of the present invention can
be implemented in a variety of forms. Therefore, while this
invention has been described in connection with particular examples
thereof, the true scope of the invention should not be so limited
since other modifications will become apparent to the skilled
practitioner upon a study of the drawings, the specification and
the following claims.
* * * * *